4-Meth­oxy­benzamidinium nitrate

Irrera, S.; Portalone, G.

doi:10.1107/S1600536812045874

organic compounds

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Volume 68| Part 12| December 2012| Page o3334

doi:10.1107/S1600536812045874

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4-Methoxybenzamidinium nitrate

Simona Irrera ^a and Gustavo Portalone ^a ^*

^aChemistry Department, `Sapienza' University of Rome, P.le A. Moro, 5, I-00185 Rome, Italy
^*Correspondence e-mail: g.portalone@caspur.it

(Received 12 October 2012; accepted 6 November 2012; online 10 November 2012)

The title salt, C₈H₁₁N₂O⁺·NO₃⁻, was synthesized by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and nitric acid. The asymmetric unit comprises a non-planar 4-methoxybenzamidinium cation and a nitrate anion. In the cation, the amidinium group has two similar C—N bond lengths [1.302 (3) and 1.313 (3) Å] and its plane forms a dihedral angle of 32.66 (5)° with the mean plane of the benzene ring. The nitrate–amidinium ion pair is not planar, as the dihedral angle between the planes defined by the CN₂⁺ and NO₃⁻ units is 19.28 (6)°. The ionic components are associated in the crystal via N—H⋯O hydrogen bonds, resulting in a three-dimensional network.

Related literature

For the biological and pharmacological relevance of benzamidine, see: Powers & Harper (1999 ); Grzesiak et al. (2000 ). For structural analysis of proton-transfer adducts containing molecules of biological interest, see: Portalone (2011a ); Portalone & Irrera (2011 ). For the supramolecular association in proton-transfer adducts containing benzamidinium cations, see; Portalone (2010 , 2011b , 2012 ); Irrera & Portalone (2012 ); Irrera et al. (2012 ). For hydrogen-bond motifs, see: Bernstein et al. (1995 ).

Experimental

Crystal data

C₈H₁₁N₂O⁺·NO₃⁻
M_r = 213.20
Orthorhombic, P 2₁ 2₁ 2₁
a = 7.1049 (7) Å
b = 10.3558 (8) Å
c = 13.4325 (9) Å
V = 988.32 (14) Å³
Z = 4
Mo Kα radiation
μ = 0.12 mm⁻¹
T = 298 K
0.20 × 0.10 × 0.08 mm

Data collection

Oxford Diffraction Xcalibur S CCD diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006 $[Oxford Diffraction (2006). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.]$ ) T_min = 0.977, T_max = 0.991
6206 measured reflections
1253 independent reflections
989 reflections with I > 2σ(I)
R_int = 0.028

Refinement

R[F² > 2σ(F²)] = 0.038
wR(F²) = 0.083
S = 0.98
1253 reflections
154 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.12 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O1	0.87 (2)	2.00 (2)	2.850 (3)	166 (2)
N1—H1B⋯O3ⁱ	0.91 (2)	2.10 (2)	3.008 (3)	170 (2)
N2—H2A⋯O2	0.87 (2)	2.05 (2)	2.920 (3)	175 (2)
N2—H2B⋯O1ⁱⁱ	0.84 (3)	2.43 (3)	3.030 (3)	129 (2)
N2—H2B⋯O3ⁱⁱ	0.84 (3)	2.33 (3)	3.174 (3)	177 (2)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, -y+1, z+{\script{1\over 2}}]$ ; (ii) $[-x+1, y-{\script{1\over 2}}, -z-{\script{1\over 2}}]$ .

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 $[Oxford Diffraction (2006). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.]$ ); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2006 $[Oxford Diffraction (2006). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.]$ ); program(s) used to solve structure: SIR97 (Altomare et al., 1999 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ); molecular graphics: ORTEP-3 (Farrugia, 2012 ); software used to prepare material for publication: WinGX (Farrugia, 2012).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536812045874/fi2127sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812045874/fi2127Isup2.hkl

checkCIF report

Comment top

Following our on-going interest on systematic structural analysis of proton-transfer adducts containing molecules of biological interest (Portalone, 2011a; Portalone & Irrera, 2011), benzamidine derivatives, which have shown strong biological and pharmacological activity (Powers & Harper, 1999; Grzesiak et al., 2000), are being used in our group as bricks for supramolecular construction (Portalone, 2010, 2011b, 2012). Indeed, these molecules are strong Lewis bases and their cations can be easily anchored onto numerous inorganic and organic anions and polyanions, largely because of the presence of four potential donor sites for hydrogen-bonding.

We report here the crystal structure of the title compound, 4-methoxybenzamidinium nitrate, which was obtained by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and nitric acid.

The asymmetric unit of the title compound comprises one non-planar 4-methoxybenzamidinium cation and one nitrate anion (Fig. 1).

In the cation, the amidinium group forms dihedral angle of 32.66 (5)° with the mean plane of the phenyl ring, which is close to the the values observed in protonated benzamidinium ions (14.4 (1) - 30.4 (1)°, Portalone, 2010, 2012; Irrera et al., 2012). The lack of planarity in all these systems is obviously caused by steric hindrances between the H atoms of the aromatic ring and the amidine group. This conformation is rather common in benzamidinium-containing small-molecule crystal structures, with the only exception of benzamidinium diliturate, where the benzamidinium cation is planar (Portalone, 2010). The pattern of bond lengths and bond angles of the 4-methoxybenzamidinium cation agrees with that reported in previous structural investigations (Irrera et al., 2012; Portalone, 2010, 2012; Irrera & Portalone, 2012). In particular the amidinium group, true to one's expectations, features similar C—N bonds [1.302 (3) and 1.313 (3) Å], evidencing the delocalization of the π electrons and double-bond character. The molecular parameters for the nitrate ion are in the expected range.

The ionic components of compound (I) are joined by two N⁺—H···O^- (±) hydrogen bonds to form ionic dimers with graph-set motif R²₂(8) (Bernstein et al., 1995). Remarkably, at variance with the well known carboxylic dimer R²₂ (8) motif, the nitrate-amidinium pair is not planar, as the dihedral angles for the planes defined by the CN₂⁺ and NO₃^- atoms is 19.28 (6)°. Similar deviation from planarity has been previously observed in the carboxylate-amidinium pair of benzamidinium 2,6-dimethoxybenzoate (Irrera et al., 2012).

Analysis of the crystal packing of the title compound (Fig. 2) shows that each amidinium unit is bound to three nitrate anions by five distinct N—H⁺···O^- intermolecular hydrogen bonds (N⁺···O^- = 2.850 (3) - 3.174 (3) Å, Table 1). Four cation-to-anion N⁺···O^- interactions form two types of hydrogen-bonded rings: the R²₁(4), which indicates a bifurcated hydrogen bond from N2—H2b to the two acceptors (O1, O3), and the already mentioned R²₂(8) supramolecular synthon. Both these ring motifs lead to the formation of ribbons approximately along crystallographic b axis. These ribbons are then interconnected by means of the remaining N⁺···O^- intermolecular hydrogen bond.

Related literature top

For the biological and pharmacological relevance of benzamidine, see: Powers & Harper (1999); Grzesiak et al. (2000). For structural analysis of proton-transfer adducts containing molecules of biological interest, see: Portalone (2011a); Portalone & Irrera (2011). For the supramolecular association in proton-transfer adducts containing benzamidinium cations, see; Portalone (2010, 2011b, 2012); Irrera & Portalone (2012); Irrera et al. (2012). For hydrogen-bond motifs, see: Bernstein et al. (1995).

Experimental top

4-methoxybenzamidine (0.1 mmol, Fluka at 96% purity) was dissolved without further purification in 6 ml of hot water and heated under reflux for 3 h. While stirring, HNO₃ (4 mol L^-1) was added dropwise until pH reached 2. After cooling the solution to an ambient temperature, colourless crystals suitable for single-crystal X-ray diffraction were grown by slow evaporation of the solvent after one week.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis CCD (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures top

	Fig. 1. The asymmetric unit of the title compound. Displacements ellipsoids are at the 50% probability level. The asymmetric unit was selected so that the two ions are linked by N^+.—H···O^- hydrogen bonds. H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are indicated by dashed lines.
	Fig. 2. Crystal packing diagram for the title compound. All atoms are shown as small spheres of arbitrary radii. For the sake of clarity, H atoms not involved in hydrogen bonding have been omitted. Hydrogen bonding is indicated by dashed lines.

4-Methoxybenzamidinium nitrate top

Crystal data top

C₈H₁₁N₂O⁺·NO₃⁻	F(000) = 448
M_r = 213.20	D_x = 1.433 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: P 2ac 2ab	Cell parameters from 2927 reflections
a = 7.1049 (7) Å	θ = 3.0–29.0°
b = 10.3558 (8) Å	µ = 0.12 mm⁻¹
c = 13.4325 (9) Å	T = 298 K
V = 988.32 (14) Å³	Tablets, colourless
Z = 4	0.20 × 0.10 × 0.08 mm

Data collection top

Oxford Diffraction Xcalibur S CCD diffractometer	1253 independent reflections
Radiation source: Enhance (Mo) X-ray Source	989 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.028
Detector resolution: 16.0696 pixels mm^-1	θ_max = 27.0°, θ_min = 3.0°
ω and ϕ scans	h = −8→8
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006)	k = −13→12
T_min = 0.977, T_max = 0.991	l = −17→17
6206 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.083	H atoms treated by a mixture of independent and constrained refinement
S = 0.98	w = 1/[σ²(F_o²) + (0.0527P)² + 0.0001P] where P = (F_o² + 2F_c²)/3
1253 reflections	(Δ/σ)_max < 0.001
154 parameters	Δρ_max = 0.12 e Å⁻³
0 restraints	Δρ_min = −0.20 e Å⁻³

Crystal data top

C₈H₁₁N₂O⁺·NO₃⁻	V = 988.32 (14) Å³
M_r = 213.20	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 7.1049 (7) Å	µ = 0.12 mm⁻¹
b = 10.3558 (8) Å	T = 298 K
c = 13.4325 (9) Å	0.20 × 0.10 × 0.08 mm

Data collection top

Oxford Diffraction Xcalibur S CCD diffractometer	1253 independent reflections
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006)	989 reflections with I > 2σ(I)
T_min = 0.977, T_max = 0.991	R_int = 0.028
6206 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.038	0 restraints
wR(F²) = 0.083	H atoms treated by a mixture of independent and constrained refinement
S = 0.98	Δρ_max = 0.12 e Å⁻³
1253 reflections	Δρ_min = −0.20 e Å⁻³
154 parameters

Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O4	0.3500 (3)	0.10530 (16)	0.33730 (12)	0.0565 (5)
N1	0.3218 (3)	0.3966 (2)	−0.07851 (16)	0.0441 (5)
H1A	0.325 (3)	0.426 (2)	−0.1390 (18)	0.041 (6)*
H1B	0.268 (3)	0.448 (2)	−0.0308 (18)	0.044 (7)*
N2	0.4153 (3)	0.1984 (2)	−0.12938 (16)	0.0454 (5)
H2A	0.408 (3)	0.222 (3)	−0.1914 (18)	0.046 (7)*
H2B	0.463 (3)	0.127 (3)	−0.1138 (17)	0.045 (8)*
C1	0.3682 (3)	0.2331 (2)	0.04594 (15)	0.0359 (5)
C2	0.4110 (3)	0.3182 (2)	0.12224 (14)	0.0377 (5)
H2	0.4426	0.4032	0.1072	0.045*
C3	0.4073 (3)	0.2785 (2)	0.22025 (16)	0.0419 (5)
H3	0.4372	0.3363	0.2708	0.050*
C4	0.3588 (3)	0.1520 (2)	0.24330 (16)	0.0397 (5)
C5	0.3158 (3)	0.0660 (2)	0.16755 (17)	0.0432 (5)
H5	0.2832	−0.0188	0.1827	0.052*
C6	0.3215 (3)	0.1061 (2)	0.07021 (17)	0.0401 (5)
H6	0.2937	0.0478	0.0197	0.048*
C7	0.3686 (3)	0.2769 (2)	−0.05791 (15)	0.0347 (5)
C8	0.3767 (4)	0.1947 (3)	0.41712 (18)	0.0639 (8)
H8A	0.498 (3)	0.2338 (16)	0.4114 (9)	0.096*
H8B	0.368 (3)	0.1501 (8)	0.4793 (11)	0.096*
H8C	0.282 (2)	0.2602 (17)	0.4141 (9)	0.096*
N3	0.3829 (3)	0.3901 (2)	−0.35182 (15)	0.0471 (5)
O1	0.3880 (3)	0.46641 (18)	−0.28077 (14)	0.0669 (5)
O2	0.3696 (3)	0.27255 (18)	−0.33771 (13)	0.0735 (6)
O3	0.3962 (3)	0.43439 (17)	−0.43752 (12)	0.0611 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O4	0.0789 (12)	0.0439 (10)	0.0466 (9)	−0.0041 (10)	0.0002 (8)	0.0075 (9)
N1	0.0525 (12)	0.0399 (12)	0.0401 (11)	0.0049 (10)	0.0049 (9)	0.0023 (10)
N2	0.0481 (12)	0.0456 (14)	0.0425 (12)	0.0050 (11)	0.0003 (9)	−0.0013 (10)
C1	0.0272 (10)	0.0357 (12)	0.0448 (11)	0.0026 (9)	0.0010 (9)	−0.0008 (10)
C2	0.0386 (12)	0.0279 (12)	0.0466 (12)	−0.0024 (9)	−0.0005 (9)	−0.0001 (10)
C3	0.0477 (13)	0.0346 (11)	0.0433 (11)	−0.0016 (11)	−0.0055 (10)	−0.0071 (11)
C4	0.0403 (12)	0.0363 (12)	0.0426 (11)	0.0034 (10)	0.0002 (9)	0.0048 (11)
C5	0.0460 (13)	0.0297 (12)	0.0537 (13)	−0.0028 (11)	0.0043 (11)	0.0007 (11)
C6	0.0370 (11)	0.0345 (12)	0.0488 (12)	−0.0006 (10)	−0.0001 (10)	−0.0055 (11)
C7	0.0264 (10)	0.0359 (12)	0.0416 (11)	0.0001 (9)	0.0020 (9)	−0.0032 (11)
C8	0.0867 (19)	0.0635 (18)	0.0415 (12)	−0.0123 (17)	−0.0007 (13)	0.0001 (13)
N3	0.0480 (11)	0.0489 (12)	0.0446 (10)	0.0027 (10)	−0.0002 (10)	0.0090 (11)
O1	0.0978 (14)	0.0531 (11)	0.0498 (9)	0.0019 (11)	0.0058 (10)	0.0028 (9)
O2	0.1182 (17)	0.0438 (11)	0.0586 (10)	−0.0156 (12)	−0.0060 (12)	0.0124 (9)
O3	0.0836 (12)	0.0565 (11)	0.0434 (9)	0.0070 (10)	0.0062 (9)	0.0164 (9)

Geometric parameters (Å, º) top

O4—C4	1.354 (3)	C3—C4	1.390 (3)
O4—C8	1.429 (3)	C3—H3	0.9300
N1—C7	1.313 (3)	C4—C5	1.387 (3)
N1—H1A	0.87 (2)	C5—C6	1.373 (3)
N1—H1B	0.91 (2)	C5—H5	0.9300
N2—C7	1.302 (3)	C6—H6	0.9300
N2—H2A	0.87 (2)	C8—H8A	0.9572
N2—H2B	0.84 (3)	C8—H8B	0.9572
C1—C2	1.386 (3)	C8—H8C	0.9572
C1—C6	1.395 (3)	N3—O2	1.235 (3)
C1—C7	1.467 (3)	N3—O1	1.240 (3)
C2—C3	1.379 (3)	N3—O3	1.243 (2)
C2—H2	0.9300

C4—O4—C8	117.53 (18)	C6—C5—C4	119.9 (2)
C7—N1—H1A	121.4 (16)	C6—C5—H5	120.1
C7—N1—H1B	120.3 (14)	C4—C5—H5	120.1
H1A—N1—H1B	118 (2)	C5—C6—C1	121.0 (2)
C7—N2—H2A	120.8 (17)	C5—C6—H6	119.5
C7—N2—H2B	118.0 (16)	C1—C6—H6	119.5
H2A—N2—H2B	121 (2)	N2—C7—N1	120.0 (2)
C2—C1—C6	118.62 (19)	N2—C7—C1	120.6 (2)
C2—C1—C7	120.41 (18)	N1—C7—C1	119.49 (19)
C6—C1—C7	120.95 (19)	O4—C8—H8A	109.5
C3—C2—C1	120.8 (2)	O4—C8—H8B	109.5
C3—C2—H2	119.6	H8A—C8—H8B	109.5
C1—C2—H2	119.6	O4—C8—H8C	109.5
C2—C3—C4	119.9 (2)	H8A—C8—H8C	109.5
C2—C3—H3	120.1	H8B—C8—H8C	109.5
C4—C3—H3	120.1	O2—N3—O1	120.82 (19)
O4—C4—C5	116.40 (19)	O2—N3—O3	120.8 (2)
O4—C4—C3	123.8 (2)	O1—N3—O3	118.4 (2)
C5—C4—C3	119.8 (2)

C6—C1—C2—C3	−0.1 (3)	C3—C4—C5—C6	0.1 (3)
C7—C1—C2—C3	178.67 (18)	C4—C5—C6—C1	−0.6 (3)
C1—C2—C3—C4	−0.5 (3)	C2—C1—C6—C5	0.6 (3)
C8—O4—C4—C5	−174.4 (2)	C7—C1—C6—C5	−178.10 (19)
C8—O4—C4—C3	5.5 (3)	C2—C1—C7—N2	148.0 (2)
C2—C3—C4—O4	−179.38 (19)	C6—C1—C7—N2	−33.3 (3)
C2—C3—C4—C5	0.5 (3)	C2—C1—C7—N1	−31.7 (3)
O4—C4—C5—C6	179.9 (2)	C6—C1—C7—N1	147.0 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1	0.87 (2)	2.00 (2)	2.850 (3)	166 (2)
N1—H1B···O3ⁱ	0.91 (2)	2.10 (2)	3.008 (3)	170 (2)
N2—H2A···O2	0.87 (2)	2.05 (2)	2.920 (3)	175 (2)
N2—H2B···O1ⁱⁱ	0.84 (3)	2.43 (3)	3.030 (3)	129 (2)
N2—H2B···O3ⁱⁱ	0.84 (3)	2.33 (3)	3.174 (3)	177 (2)

Symmetry codes: (i) −x+1/2, −y+1, z+1/2; (ii) −x+1, y−1/2, −z−1/2.

Experimental details

Crystal data
Chemical formula	C₈H₁₁N₂O⁺·NO₃⁻
M_r	213.20
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	298
a, b, c (Å)	7.1049 (7), 10.3558 (8), 13.4325 (9)
V (Å³)	988.32 (14)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.12
Crystal size (mm)	0.20 × 0.10 × 0.08

Data collection
Diffractometer	Oxford Diffraction Xcalibur S CCD diffractometer
Absorption correction	Multi-scan (CrysAlis RED; Oxford Diffraction, 2006)
T_min, T_max	0.977, 0.991
No. of measured, independent and observed [I > 2σ(I)] reflections	6206, 1253, 989
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.639

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.038, 0.083, 0.98
No. of reflections	1253
No. of parameters	154
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.12, −0.20

Computer programs: CrysAlis CCD (Oxford Diffraction, 2006), CrysAlis RED (Oxford Diffraction, 2006), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 2012), WinGX (Farrugia, 2012).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1	0.87 (2)	2.00 (2)	2.850 (3)	166 (2)
N1—H1B···O3ⁱ	0.91 (2)	2.10 (2)	3.008 (3)	170 (2)
N2—H2A···O2	0.87 (2)	2.05 (2)	2.920 (3)	175 (2)
N2—H2B···O1ⁱⁱ	0.84 (3)	2.43 (3)	3.030 (3)	129 (2)
N2—H2B···O3ⁱⁱ	0.84 (3)	2.33 (3)	3.174 (3)	177 (2)

Symmetry codes: (i) −x+1/2, −y+1, z+1/2; (ii) −x+1, y−1/2, −z−1/2.

References

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Volume 68| Part 12| December 2012| Page o3334

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